of places and for many different reasons. One of the nest studied (and most severe) examples was the introduction of Nile perch into Lake Victoria. Since the 1960s the Nile perch gradually exterminated the 500 species of cichlid fishes found only in this lake and nowhere else. Some species survive now only in captive breeding programmes, but others are probably extinct.[37] Carp, tilapia, European perch, brown trout, rainbow trout, and sea lampreys are other examples of fish that have caused problems by being introduced into alien environments.